Typically, drive splines between an internally splined turbine engine drive shaft and an externally splined accessory driven shaft are lubricated by a supply of oil trapped in an annular reservoir. The annular reservoir is defined diametrally by an inside surface of the drive shaft defining an outside diameter of the reservoir and an inside diameter of an internal dam defining an inside diameter of the reservoir. The annular reservoir is defined axially by the internal dam within the drive shaft and by a seal between the drive shaft and the driven shaft. The internal dam is located beyond a point of maximum travel of the driven shaft into the drive shaft. The seal is located on an outside diameter of the driven shaft to seal against the drive shaft at a second end of the drive shaft near where the driven shaft enters the drive shaft.
Deterioration or loss of the seal results in oil leaving the annular reservoir. If the oil in the annular reservoir is continuously replenished during the operation of the engine, the fluid supplied to the annular reservoir will flow past the unsealed end of the drive shaft.